Abstract

Introduction: It is well known that microorganism in dry environment have significantly higher heat resistance than similar microorganisms in an environment with higher available water.
Purpose: The aim of this experiment is to determine the effect of added water and steam on the heat resistance of E. faecium inoculated on selected low moisture products (blanched peanuts, cashews, pumpkin seeds, red-skin peanuts, and walnuts.

Methods: Products were artificially inoculated with E. faecium and dried for 24 hours. With the use of a pilot scale batch oven, the heat resistance of E. faecium inoculated on the products was evaluated under three different conditions, (1) dry products exposed to dry heat at 160°C for 25 minutes, (2) wet products (dry product with 10% sterile water added) exposed to dry heat at 160°C for 25 minutes and (3) dry products exposed to steam at 160°C for 10 minutes.
Results: After artificial inoculation and drying level of E. faecium on products (n = 6) prior to heat treatment were 8.56 Log CFU/g (blanched peanuts), 9.00 Log CFU/g (cashew nuts), 8.70 Log CFU/g (pumpkin seeds), 8.30 log CFU/g (red-skin peanuts) and 7.26 Log CFU/g (walnuts). The result of the heat treatment showed a significance different (P ≤ 0.01) between the use of dry heat and the use of wet product and steam. After heat treatment log reduction (n = 6) achieved for (1) dry products exposed to dry heat ranged from 4.98 to 6.11 log CFU/g, (2) wet products exposed to dry heat ranged from 6.95 to 7.70 Log CFU/g and (3) dry products exposed to steam ranged from 6.95 to 7.60 log CFU/g.
Significance: The result obtained in this study confirms that dry microbial cells have significantly greater heat resistance that cells in an environment where water activity is close to one (1).